May 2008
Volume 49, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2008
Corneal Refractive Index Changes in Keratoconus
Author Affiliations & Notes
  • J. Schallhorn
    USC Keck School of Medicine, Los Angeles, California
  • M. Tang
    Ophthalmology-USC, Doheny Eye Institute, Los Angeles, California
  • Y. Li
    Ophthalmology-USC, Doheny Eye Institute, Los Angeles, California
  • D. Huang
    Ophthalmology-USC, Doheny Eye Institute, Los Angeles, California
  • Footnotes
    Commercial Relationships  J. Schallhorn, None; M. Tang, Optovue, Inc., F; Optovue, Inc., P; Y. Li, None; D. Huang, Optovue, Inc., R; Optovue, Inc., F; Optovue, Inc., I; Optovue, Inc., C; Carl Zeiss Meditec, Inc., P; Optovue, Inc., P.
  • Footnotes
    Support  NIH grants R01 EY018184-01, P30 EY03040; Research to Prevent Blindness; Optovue, Inc.
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 4345. doi:https://doi.org/
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    • Get Citation

      J. Schallhorn, M. Tang, Y. Li, D. Huang; Corneal Refractive Index Changes in Keratoconus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4345. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: : To study the effect of keratoconus on the corneal index using optical coherence tomography (OCT) and Orbscan.

Methods: : 12 eyes of 8 patients with keratoconus and 25 eyes of 16 normal patients were imaged using the Orbscan slit-scanning device and the Visante OCT device. The central corneal thickness was measured with both instruments and the ratio was calculated. According to optical principles, the apparent corneal thickness measured by OCT scales in direct proportion to the group index and the apparent corneal thickness measured by slit-scanning scales inversely with the refractive index.

Results: : The ratio of the OCT/Orbscan central pachymetry in normal eyes is 0.986 ±0.030 and the ratio in keratoconic eyes is 1.011±0.034. The two are significantly different from each other (p=0.042). Assuming the group and refractive indices changes equally, keratoconus increase index by 1.3% on the average.

Conclusions: : Keratoconus appears to increase the corneal index. One possible mechanism is increased corneal stress and strain due to the ectasia. This might lead to more tightly packed collagen lamellae and higher refractive and group indices.

Keywords: keratoconus • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • cornea: stroma and keratocytes 
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